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Catadioptric Optical System And Exposure Apparatus Having The Same - Patent 6717722

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United States Patent: 6717722


































 
( 1 of 1 )



	United States Patent 
	6,717,722



 Shafer
,   et al.

 
April 6, 2004




 Catadioptric optical system and exposure apparatus having the same



Abstract

A projection exposure lens system has an object side catadioptric system,
     and intermediate image and a refractive lens system. The refractive lens
     system from its intermediate image side and in the direction of its image
     plane has a first lens group of positive refractive power, a second lens
     group of negative refractive power, a third lens group of positive
     refractive power, a fourth lens group of negative refractive power, and a
     fifth lens group of positive refractive power.


 
Inventors: 
 Shafer; David R. (Fairfield, CT), Beierl; Helmut (Heidenheim, DE), Furter; Gerhard (Ellwangen, DE), Schuster; Karl-Heinz (Konigsbronn, DE), Ulrich; Wilhelm (Aalen, DE) 
 Assignee:


Zeiss; Car
 (Heidenheim (Brenz), 
DE)





Appl. No.:
                    
 10/079,964
  
Filed:
                      
  February 20, 2002

 Related U.S. Patent Documents   
 

Application NumberFiling DatePatent NumberIssue Date
 364382Jul., 1999
 

 



  
Current U.S. Class:
  359/355  ; 359/364; 359/365; 359/366
  
Current International Class: 
  G02B 17/08&nbsp(20060101); G03F 7/20&nbsp(20060101); G02B 013/14&nbsp()
  
Field of Search: 
  
  










 359/355,364,365,366,727,728,732,350,356,357,726
  

References Cited  [Referenced By]
U.S. Patent Documents
 
 
 
5323263
June 1994
Schoenmakers

5592329
January 1997
Ishiyama et al.

5689377
November 1997
Takahashi

5691802
November 1997
Takahashi

5694241
December 1997
Ishiyama et al.

5844728
December 1998
Hashimoto et al.

5861997
January 1999
Takahashi

6392822
May 2002
Takahashi



 Foreign Patent Documents
 
 
 
8-62502
Aug., 1994
JP



   Primary Examiner:  Sikder; Mohammad



Parent Case Text



This application is a Division of Ser. No. 09/364,382 filed Jul. 29, 1999
     now U.S. Pat. No. 6,496,306 which claims benefit of Ser. No. 60/094,579
     filed Jul. 29, 1998.

Claims  

We claim:

1.  A projection exposure lens system, comprising: an object side catadioptric system, an intermediate image, and a refractive lens system, with lenses made of a first material and
lenses made of a second material, in which no more than four lenses are made of said second material.


2.  The projection exposure lens system according to claim 1, in which no more than three lenses are made of said second material.


3.  A projection exposure lens system, according to claim 1, in which said catadioptric system has at least one deflecting element, a concave mirror and a plurality of lenses between said at least one deflecting element and said concave mirror,
and in which said concave mirror and all lenses arranged between said deflecting element and said concave mirror are arranged in a compact unit.


4.  A projection exposure lens system, according to claim 1, in which said catadioptric system has at least one deflecting element, a concave mirror and a plurality of lenses, and in which said catadioptric system has at least one positive lens
between said object side and a first deflecting element, and not more than one positive and not more than three negative lenses between said first deflecting element and said concave mirror.


5.  A projection exposure lens system according to claim 1, in which said refractive lens system from its intermediate image side and in the direction of its image plane has a first lens group of positive refractive power, a second lens group of
negative refractive power, a third lens group of positive refractive power, a fourth lens group of negative refractive power, and a fifth lens group of positive refractive power.


6.  A projection exposure lens system according to claim 1, in which at least one -+ power doublet with a negative power lens and a positive power lens in this sequence from said object side is arranged in said refractive lens system.


7.  A projection exposure lens system according to claim 1, in which said refractive lens system comprises a field lens group, an intermediate correcting lens group and a focussing lens group.


8.  A projection exposure lens system according to claim 1, in which said catadioptric system has an imaging ratio of greater than 0.95, and different from unity.


9.  The projection exposure lens system according to claim 1, in which said refractive lens system contains at least a pair of menisci, the convex surface of an intermediate-image-side meniscus facing said intermediate image, the convex surface
of the other menisci facing oppositely.


10.  The projection exposure lens system according to claim 9, in which said at least one pair of menisci is arranged in a correcting lens group.


11.  The projection exposure lens system according to claim 7, in which one of said -+ power doublets is arranged in a focussing lens group.


12.  The projection exposure lens system according to claim 7, in which one of said -+ power doublets is arranged next to a system aperture.


13.  The projection exposure lens system according to claim 1, in which no more than one lens of said catadioptric system is made of said second lens material.


14.  The projection exposure lens system according to claim 1, in which the diameter of lenses made of said second lens material does not exceed the 0.85 fold of the diameter of a biggest optical element.


15.  The projection exposure lens system according to claim 1, in which the diameter of lenses made of said second lens material does not exceed 220 mm.


16.  The projection exposure lens system according to claim 1, in which said catadioptric system contains no more than six lenses.


17.  The projection lens system according to claim 16, in which said catadioptric system contains no more than five lenses.


18.  The projection exposure lens system according to claim 1, in which longitudinal chromatic aberration is less than 0.015 .mu.m per a band width of 1 pm at 193 nm.


19.  The projection exposure lens according to claim 1, in which longitudinal chromatic aberration is less than 0.05 .mu.m per a band width of 1 pm at 157 nm.


20.  The projection exposure lens system according to claim 1, in which the imaging ratio of said catadioptric system is greater than 0.8.


21.  The projection exposure lens system according to claim 21, in which said imaging ratio of said catadioptric system is greater than 0.95.


22.  The projection exposure lens according to claim 1, in which in said refractive lens system all lenses made of said second lens material are arranged in a converging light beam next to an image plane.


23.  The projection exposure lens system according to claim 1, in which said projection exposure lens system is both side telecentric.


24.  The projection exposure lens system according to claim 7, having at least one beam waist in a refracting subsystem, and said -+ power doublets are arranged behind a last beam waist.


25.  The projection exposure lens system according to claim 7, in which said -+ doublets are arranged such that a light beam diameter inside lens elements of said -+doublets is more than 80% of a maximum beam diameter.


26.  The projection exposure lens system according to claim 1, further comprising a concave mirror in said catadioptric system, and a reflecting prism inserted for reflection of a light beam between an object and said concave mirror.


27.  The projection exposure lens system according to claim 1, in which said projection exposure lens system is designed for use with one of 248 nm and 193 nm light and said first material comprises fused silica and said second material comprises
calcium fluoride.


28.  The projection exposure lens system according to claim 1, in which said first material comprises calcium fluoride.


29.  The projection exposure lens system according to claim 1, further comprising a first deflecting element in said catadioptric system, in which exactly one lens is placed between an object and said first deflecting element.


30.  The projection exposure lens system according to claim 29, in which the ratio of focal length of said one lens before said first deflecting mirror over the distance from said one lens to said concave mirror is unity within (+/-) fifteen
percent.


31.  A projection exposure apparatus, comprising: a projection exposure lens system according to claim 1, an excimer laser light source, an illuminating system, a mask handling and positioning system, and a wafer handling and positioning system.


32.  A method of producing microstructured devices by lithography comprising using a projection exposure apparatus according to claim 31.


33.  The method according to claim 32, further comprising using one of step and repeat, scanning, and stitching exposure schemes.  Description  

BACKGROUND OF THE INVENTION


1.  Field of the Invention


The present invention relates to a projection exposure lens in a projection exposure apparatus such as a wafer scanner or a wafer stepper used to manufacture semiconductor elements or other microstructure devices by photolithography and, more
particularly, to a catadioptric projection optical lens with an object side catadioptric system, an intermediate image and a refractive lens system for use in such a projection exposure apparatus.


2.  Related Background Art


U.S.  Pat.  No. 4,779,966 to Friedman gives an early example of such a lens, however the catadioptric system being arranged on the image side.  Its development starting from the principle of a Schupmann achromat is described.  It is an issue of
this patent to avoid a second lens material, consequently all lenses are of fused silica.  Light source is not specified, band width is limited to 1 nm.


U.S.  Pat.  No. 5,052,763 to Singh (EP 0 475 020) is another example.  Here it is relevant that odd aberrations are substantially corrected separately by each subsystem, wherefore it is preferred that the catadioptric system is a 1:1 system and
no lens is arranged between the object and the first deflecting mirror.  A shell is placed between the first deflecting mirror and the concave mirror in a position more near to the deflecting mirror.  All examples provide only fused silica lenses.  NA is
extended to 0.7 and a 248 nm excimer laser or others are proposed.  Line narrowing of the laser is proposed as sufficient to avoid chromatic correction by use of different lens materials.


U.S.  Pat.  No 5,691,802 to Takahashi is another example, where a first optical element group having positive refracting power between the first deflecting mirror and the concave mirror is requested.  This is to reduce the diameter of the mirror,
and therefore this positive lens is located near the first deflecting mirror.  All examples show a great number of CaF.sub.2 lenses.


EP 0 736 789 A to Takahashi is an example, where it is requested that between the first deflecting mirror and the concave mirror three lens groups are arranged, with plus minus plus refractive power, also with the aim of reducing the diameter of
the concave mirror.  Therefore, the first positive lens is located rather near to the first reflecting mirror.  Also many CaF.sub.2 lenses are used for achromatization.


DE 197 26 058 A to Omura describes a system where the catadioptric system has a reduction ratio of 0.75</.beta..sub.1 /<0.95 and a certain relation for the geometry of this system is fulfilled as well.  Also many CaF.sub.2 lenses are used
for achromatization.


For purely refractive lenses of microlithography projection exposure system a lens design where the light beam is twice widened strongly is well known, see e.g. Glatzel, E., Zeiss-Information 26 (1981), No. 92 pages 8-13.  A recent example of
such a projection lens with +-+-+ lens groups is given in EP 0 770 895 to Matsuzawa and Suenaga.


The refractive partial objectives of the known catadioptric lenses of the generic type of the invention, however show much simpler constructions.


The contents of these documents are incorporated herein by reference.  They give background and circumstances of the system according to the invention.


SUMMARY OF THE INVENTION


It is an object of the present invention to obtain a catadioptric optical system of new construction principles allowing for large numerical aperture, large image field, sufficient laser bandwidth, solid and stable construction, which takes into
account the present limitations on availability of CaF.sub.2 in quantity and quality.  This holds for a DUV projection lens and gives the basis for a one material only lens for VUV (157 nm).


In order to achieve the above object, according to the present invention, there is provided a projection exposure lens according to one of claims 1 to 7 or any combination of them as claimed in claim 8.


Advantageous versions are obtained when including features of one or more of the dependent claims 8 to 28.


An advantageous projection exposure apparatus of claim 29 is obtained by incorporating a projection exposure lens according to at least one of claims 1 to 28 into a known apparatus.


A method of producing microstructured devices by lithography (claim 30) according to the invention is characterized by the use of a projection exposure apparatus according to the preceeding claim 29.  Claim 31 gives an advantageous mode of this
method.


The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention. 
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter.  However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of
the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description. 

BRIEF DESCRIPTION OF THE
DRAWINGS


FIG. 1 is a view showing the arrangement of an exposure apparatus to which a catadioptric optical system according to the present invention can be applied;


FIG. 2 is a section view of the lens arrangement of a first embodiment;


FIG. 3 is a section view of the lens arrangement of a second embodiment;


FIG. 4 is a section view of the lens arrangement of a third embodiment;


FIG. 5 is a section view of the lens arrangement of a fourth embodiment;


FIG. 6a is a section view of the lens arrangement of a fifth embodiment;


FIG. 6b is a representation of an imaging error of the fifth embodiment; and


FIG. 7 is a schematic section view of part of the lens arrangement of a sixth embodiment. 

The projection exposure apparatus as schematically shown in FIG. 1 includes an excimer laser light source 1 with an arrangement 11 moderately
narrowing bandwidth.  An illumination system 2 produces a large field, sharply limited and illuminated very homogeneously, which matches the telecentricity requirements of the projection lens, and with an illumination mode to choice.  Such mode may be
conventional illumination of variable degree of coherence, annular or quadrupole illumination.


A mask 3 is displaced in the illuminated area by a mask holding and handling system 31, which includes the scanning drive in case of a wafer scanner projection exposure apparatus.  Subsequently follows the catadioptric projection exposure lens 4,
according to the invention to be described in detail subsequently.


This lens 4 produces a reduced scale image of the mask 3 on a wafer 5.  The wafer 5 is held, handled and eventually scanned by unit 51.


All systems are controlled by control unit 6.  Such unit and the method of its use is known in the art of microlithographic projection exposure.


However, for exposure of structures in the regime of about 0.2 .mu.m and less resolution at high throughput there is a demand for various projection exposure lenses capable to be operated at 193 nm, eventually also at 248 nm or 157 nm excimer
laser wavelengths with reasonably available bandwidths (e.g. 15 pm at 193 nm), at high image side numerical aperture of 0.65 to 0.8 or more and with reasonably large rectangular or circular scanning image fields of e.g. 7.times.20 to 10.times.30
mm.sup.2.


Catadioptric systems of the type cited above are in principle suitable for this.


However, according to the invention a number of measures and features has been found to improve these systems.


The example shown in the sectional view of FIG. 2 has the lens data given in Table 1 and makes use only of fused silica lenses.  As only one lens material is used, this design can easily be adapted for other wavelengths as 248 nm or 157 nm.


The intermediate image IMI is freely accessible, so that it is easily possible to insert a field stops.  The aperture stop AP is located between lens surfaces 239 and 240 and is also well accessible.


The deflecting mirrors DM1 and DM2 in the catadioptric system CS are defined in their geometry by the demands of separation of the light beams to and from the concave mirror 209 and of clearance from lens 201, 202.  It is advantageous, that the
mirror angle of mirror DM1 differs from 45.degree., such that the beam deflection angle is greater than 90.degree..  This helps to ascertain large free working distance as well as wide clearance for the light beam relative to the first lens element 201,
202 and also gives full clearance of the lens barrel of the catadioptric systems CS from the object plane 0.


The arrangement of the two deflection mirrors DM1, DM2 allows for a straight optical axis and parallel situation of origin plane 0 and image plane IM, i.e. mask and wafer are parallel and can easily be scanned.  However, one of the deflecting
mirrors DM1, DM2 can be abandoned or eventually be replaced by a deflecting mirror in the refractive lens RL, e.g. in the air space between lens surfaces 225 and 226.  It is also clear that the deflecting mirrors can be replaced by other deflecting
optical elements (as e. g. the prism in embodiment 6 or others).


A moderate positive lens 201, 202 is placed near the origin plane 0 in the single pass beam area.  Its focal length is approximately equal to its distance from the concave mirror 209.  This makes that the concave mirror 209 is situated in a pupil
plane and thus the diameter required is minimized.


A second positive lens is located in the doubly passed area between the deflecting mirrors DM1, DM2 and the concave mirror 209.  As the production conditions of concave mirrors of 200 mm to 300 mm diameter give no strong preference to smaller
units--in contrast to lenses, namely such made from CaF.sub.2, where inhomogeneties etc. give strong limitations--there is no need to use this positive lens 203, 204 for reduction of the radius of the concave mirror 209.  It is located nearer to the
concave mirror 209 than to the first reflection mirror DM1 at a location where it serves best to minimize imaging errors.


The two negative menisci 205, 206; 207, 208 cooperate with the concave mirror 209 in a known manner, giving increased angles of incidence and stronger curvature, thus stronger correcting influence of the concave mirror 209.


It is significant, that the number of lenses in the doubly passed area of the catadioptric system CS is restricted to three, as here every lens counts doubly with respect to system energy transmission and wavefront quality degradation--without
giving more degrees of freedom for correction.


Of a total reduction ratio of .beta.=0.25 the catadioptric system CS delivers its part of .beta..sub.cs =1.008.


At the intermediate image plane IMI preferably a field stop FS is inserted, which reduces stray light favourably.


The refractive lens RL following to the intermediate image IMI is of more elaborate design than usual in the art.  It is more of a quality as fully refractive projection exposure lenses of recent developments tend to be.


One can see that the five lens group design known from sophisticated refractive microlithography lens designs featuring two waists and three bellies with +-+-+ lens groups in this sequence is adopted.  Though the first two bellies (lens surfaces
210 to 219, 224 to 227) are not very strongly expressed, the two waists W1, W2 are significantly established, each by a pair of negative menisci 220, 221; 222, 223 and 228, 229; 230, 231, whose convex surfaces face outwardly.


It is known that these lens groups at the waists W1, W2 as the others can be developed further by incorporating more lenses, e.g. to increase the numerical aperture or the image area.


From another point of view, the refractive lens RL is composed of a field lens group (lens surfaces 210 to 219) of positive power for turning the diverging chief ray into a converging chief ray, an image side positive focussing lens group (lens
surfaces 232 to 251) which generates the required large numerical aperture, and intermediately arranged lens elements, which correct imaging errors, especially including sets of oppositely arranged negative menisci (w1, w2).


The -+ power doublets with surfaces 235 to 238 and 239 to 242 are the key to the wide spectral bandwidth at good correction of the chromatic variation in spherical aberration, which is the main residual aberration in these designs.  It was found
that the alternative arrangement there of +- power doublets gives much worse chromatic variation of spherical aberration.  Here a value of 0.35 .mu.m is obtained at 15 pm laser bandwidth.


This example of FIG. 2 is suitable for printing microstructures at a resolution of less than 0.2 .mu.m over an image field of 30.times.7 mm.sup.2 rectangle at 6 mm off axis, with an excimer laser source of 0.015 nm bandwidth.


FIG. 3 and Table 2 show a design variant.  The catadioptric system CS remains very similar, however its reduction ratio now is less than unity at .beta..sub.cs =0.944.


In the refractive lens the second lens 212, 213 of FIG. 2 is abandoned, while the thick negative lens 245, 246 is split into three units 342, 343; 344, 345; 346, 347.


Also two lenses now are made of CaF.sub.2, namely the elements with the surfaces 342, 343 and 348, 349.  Related to the diameter of the greatest lens 330, 331 of ca.  250 mm their diameters of ca.  205 mm and approx. 165 mm are less than 0.81
fold and 0.67 fold.  Therefore, their dimension is not too great and effective production is ascertained.


Also they both are arranged in the converging light beam in the fifth lens group after the third belly, near the image plane.  They help with achromatization.  The other features are quite similar as those of the example of FIG. 2, including e.g.
the -+ power doublets 332 to 339.


FIG. 4 and table 3 show another example of a catadioptric lens according to the invention.


Now, the catadioptric system CS shows a major revision, as all lenses in the doubly passed region are combined into a single lens group next to the concave mirror 411.  It includes the positive lens 403, 404 and three negative lenses 405 to 410. 
Change from two to three such negative lenses provides smoother increase of beam angles and thus optimizes correction.  Thus, the construction of the lens barrel of the catadioptric system CS is simplified.  The lenses 403 to 410 and the mirror 411 can
be mounted in a compact unit of conventional construction as known from refractive projection exposure lenses.  The long distance to the deflecting mirrors DM1, DM2 can be bridged by a thermally stable tubular body, e.g. made of fiber compound, glass
ceramics or a bi-metal compound structure.


The positive lens 403, 404 now is made of fluorite (ca.  200 mm dia.), thus helping in achromatization.  It is significant for the invention, that at most three to four lenses in total made of a second material are sufficient to provide good
achromatization in this basic design.


The reduction ratio of the catadioptric system is .beta..sub.cs =0.931.  The refractive lens system is constructed very similar to the one of table 2.


A fourth embodiment is given in FIG. 5 and table 4.


Now the catadioptric system CS again is free of any CaF.sub.2 element.  Its principal construction with a compact unit of one positive (503, 504), three negative lenses (505-510) and the concave mirror 511 in one compact unit remains the same as
in the third embodiment.  The reduction ratio .beta..sub.cs is 0.961 in the most preferred range.


Also the refractive lens RL is of the same overall design as the before mentioned examples.  However, the use of CaF.sub.2 lens elements has a novel character: While lens element 544, 545 in a known manner serves for achromatization, the reason
for use of CaF.sub.2 in the two lenses 552, 553; 554, 555 next to the image plane IM is another one:


The reason for use of CaF.sub.2 here is the reduction of the "compaction" degradation effect which is rather strong with fused silica lenses at high light intensity and strong asymmetry (caused by narrow scanning image field) at 193 nm
wavelength, but far less with CaF.sub.2 lenses (or other crystalline material).


With an overall length--object 0 to image IM--of 1455 mm, a deviation off the axis of the concave mirror 511 of 590 mm, diameter of the concave mirror 511 of 250 mm, greatest lens diameter in the refractive lens system RL of 240 mm (at lens 534,
535) and diameters of the CaF.sub.2 lenses of 195 mm (544, 545), 135 mm (552, 553) and 85 mm (554, 555) the dimensions of this construction are very acceptable.  At Lambda=193 nm, 15 pm band width, reduction ratio 0.25, numerical aperture of 0.7, an
image field of 26.times.9 mm.sup.2 rectangular is imaged at a resolution of better than 0.20 .mu.m.


A fifth embodiment is given in FIG. 6a and table 5.  This is distinguished from embodiment 4 in that only the last two lenses C1, C2 (654, 655; 656, 657 are made of CaF.sub.2 with the aim of reduction of long-time degradation by compaction of
fused silica under 193 nm radiation, but no CaF.sub.2 is used for the purpose of achromatization.


The catadioptric system CS consists of a field lens 601, 602 with a focal length f' related to its distance B to the concave mirror by f'/B=1.004.


Deflecting mirror DM1 deflects the optical axis.  Its normal is tilted with respect to the optical axis by 50.degree..  This gives better beam clearance from the field lens 601, 602 than the normal 45.degree..


The positive lens 603, 604 is combined with three negative lenses 605-610 and the concave mirror 611 into a compact unit.  The distance DM1-603 is 432 mm, compared to the distance DM1-611 to the concave mirror of 597 mm, this is 72%.


The reduction ratio of the catadioptric system .beta..sub.cs =0.9608 lies in a preferable range near unity, where the achromatizing effect of the concave mirror is best exploited as well as other imaging errors (e.g. curvature of field) are kept
small.  The positive effect on Petzval sum is very good.


However, the concept of odd aberrations correction (Singh loc.  cit.) is not adapted: At the intermediate image plane IMI the values of coma--0.1724--and distortion---0.0833--by far exceed good correction values, while at the final image plane IM
coma (-0.00098) and distortion (-0.000115) are very well corrected, as other typical errors are.


A field stop FS at the intermediate image plane IMI advantageously cuts off disturbing stray light.


According to the invention the catadioptric system is designed with very few elements in compact arrangement and its function is focussed on the implementation of the achromatizing and Petzval sum influence of the concave mirror 611.


Detailed correction is the realm of the refractive lens system RL.  This is composed of a field lens group FL (surfaces 612 to 621) and a focussing lens group FG (surfaces 634 to 655).  Correcting lens elements are inserted in between, including
two pairs of opposing negative menisci 622-625 and 630-633.  These form two beam waists W1, W2.  Thus, the +-+-+ five lens group design known from sophisticated refractive projection exposure lenses is established.


The focussing lens group FG hosts the system aperture AP as well as two -+power lens groups PG1 and PG2 with the above mentioned advantages.


No achromatizing CaF.sub.2 lens is provided, but as in embodiment 4 the two lenses C1, C2 (654-657) located next the image plane IM are made of CaF.sub.2 for the above mentioned reason of avoidance of compaction.


At a length 0-IM of 1400 mm and a sideward deviation of 590 mm to the concave mirror 611, the diameter of the concave mirror 611 (and the neighboring lens 609, 610) is limited to 252 mm, while the largest lens 636, 637 of the refractive lens
system RL has a diameter of 240 mm and the CaF.sub.2 lenses have only 130 mm (C1) and 85 mm (C2) diameter.  Thus requirements of production to avoid extreme diameters are well fulfilled.


FIG. 6b shows the longitudinal spherical aberration and its chromatic variation at Lambda=193.30 nm.+-.0.015 nm for this embodiment 5, which as before mentioned is the remnant imaging error limiting the performance of this system.


It can be seen that with a moderately narrowed excimer laser source of Lambda=193.3 nm with 15 pm band width a rectangular field of 26.times.9 mm can be imaged at a resolution of better than 0.2 .mu.m.


A sixth embodiment is shown in FIG. 7 and table 6.  Here, a deflecting prism DP is inserted for deflecting the light path towards the concave mirror 711.


Since the light rays inside the prism DP spread apart less than when they are in air (or nitrogen or helium), the field size can be increased by a certain amount without introducing any vignetting of the light rays by the prism edges.  The
importance of this design modification increases at higher numerical Aperture.  Vignetting of rays limits how large a field size can be handled by the folding elements, and even a relatively small increase in field size is very desirable--for a variety
of reasons, including the possibility of shrinking all lens diameters for a given field required.  It turns out not to be relevant to try this for the second flat mirror DM2.  While FIG. 7 schematically shows the deflecting mirror region, exemplary lens
data for a full system are given in table 6.  This Prism arrangement can also help to extend the free working distance or to use other mirror angles (e. g. 45.degree.).


Embodiment 7, for which design data are given in table 7, shows the possible extension of the image with side numerical aperture well beyond the 0.7 value of the other examples.  The value of NA=0.8 is not yet limiting to this type of lens.  The
overall construction is as given in the other embodiments, thus no extra drawing is needed for explanation.


Embodiment 8 with lens data of table 8 gives a pure CaF.sub.2 design for 157 nm wavelength as an example showing the possibilities of the inventive design for use with VUV wavelengths.  The overall construction is very much like FIG. 6a.


Other combinations of claimed features than explicitly described above are within the scope of the invention.


The possibilities of the Schupman achromat for achromatization with only one lens material are fully exploited in embodiments 1 and 8.  In consequence, this embodiment 8 presents the first 157 nm design of the Schupman achromat suitable for VUV
lithography.  Insertion of aspheres and consequent reduction of number and thickness of lenses will further optimize this.


A new aspect of using a second material in a lens for avoiding compaction is given in embodiments 4 to 7.


To simplify achromatization by use of a second material very few elements made from this are sufficient as embodiments 3, 4, 6 and 7 show.


Preferably the lenses between the deflecting elements and the concave mirror are arranged in a compact unit with the latter as in embodiments 3 to 8.  All lenses are more distant from the deflecting elements than from the concave mirror, their
minimal distances do not exceed their maximum thicknesses (both taken over the diameter), or the length of the compact unit does not exceed its diameter, at least not by more than 50%.  The sophisticated design of the refractive lens system as presented
allows for good correction at increased image side numerical apertures in the 0.65 to 0.85 range.


While examples are given for the scanning scheme of exposure, the invention as well is useful with step-and-repeat or stitching.  Stitching allows for specifically smaller optics.


 TABLE 1  Lambda = 193,3 nm .beta. = 0,25 NA = 0,7  No. Radius Thickness Glass  0 Infinity 40,000  201 433,823 20,000 SIO2  202 Infinity 76,000  DM1 Infinity 286,798 Angle 50,5.degree.  203 371,257 25,000 SIO2  204 855,824 216,212  205 -242,813
15,000 SIO2  206 -957,702 29,987  207 -191,563 15,000 SIO2  208 -420,744 12,000  209 267,741 Reflector  (203) 281,798  DM2 Infinity 141,534 Angle 39,5.degree.  210 341,605 45,000 SIO2  211 -302,390 0,266  212 -314,725 15,000 SIO2  213 -535,921 21,847 
214 -293,712 15,000 SIO2  215 242,074 2,808  216 253,649 50,000 SIO2  217 -418,716 1,000  218 387,621 32,000 SIO2  219 Infinity 23,536  220 338,439 20,000 SIO2  221 180,073 56,252  222 -200,452 17,000 SIO2  223 -406,872 1,000  224 830,485 35,000 SIO2 
225 -406,246 137,396  226 564,466 32,000 SIO2  227 -1292,800 1,000  228 288,764 22,000 SIO2  229 169,297 57,016  230 -189,642 28,572 SIO2  231 -398,135 81,777  232 -476,268 32,000 SIO2  233 -238,618 1,000  234 505,684 17,000 SIO2  235 259,770 13,056  236
455,638 38,000 SIO2  237 -469,418 1,000  238 236,178 15,000 SIO2  239 = AP 145,030 2,543  240 149,636 45,000 SIO2  241 1347,200 1,000  242 138,086 29,000 SIO2  243 273,919 16,837  244 -2450,800 36,643 SIO2  245 114,868 12,598  246 183,269 33,000 SIO2 
247 -427,093 0,100  248 119,177 56,567 SIO2  249 352,582 0,100  250 176,817 42,544 SIO2  251 -263,402 15,000  IM Infinity 0,000


 TABLE 2  Lambda = 193,3 nm .beta. = -0,25 NA = 0,7  No. Radius Thickness Glass  0 Infinity 40,000  301 501,959 20,000 SIO2  302 6701,736 83,000  DM1 Infinity Angle 53,00.degree.  303 -477,089 SIO2  304 -5445,982  305 282,396 SIO2  306 1204,642 
307 216,126 SIO2  308 519,194  309 298,619 Reflector  (303)  DM2 Infinity Angle 37,00.degree.  310 -277,399 SIO2  311 876,072  312 384,127 SIO2  313 -245,187  314 -297,630 SIO2  315 778,473  316 -422,020 SIO2  317 945,111  318 -336,194 SIO2  319 -169,717 320 208,247 SIO2  321 414,789  322 -639,842 SIO2  323 420,685  324 -508,419 SIO2  325 1843,176  326 -315,017 SIO2  327 -182,247  328 197,495 SIO2  329 764,726  330 572,623 SIO2  331 246,349  332 -592,087 SIO2  333 -240,082  334 -314,738 SIO2  335 745,437 336 -219,102 SIO2  337 -178,632  338 -269,565 SIO2  339 = AP -8665,509  340 -165,739 SIO2  341 -378,291  342 -5121,046 CAF2  343 457,764  344 511,311 SIO2  345 -143,061  346 -134,125 SIO2  347 -125,446  348 -158,475 CAF2  349 451,948  350 -122,592 SIO2 
351 -830,354  352 -374,272 SIO2  353 500,000  IM Infinity


 TABLE 3  Lambda = 193,3 nm .beta. = -0,25 NA = 0,7  No. Radius Thickness Glass  0 Infinity 40,000  401 441,354 20,000 SIO2  402 -3082,575 82,000  DM1 Infinity 404,580 Angle 51.degree.  403 379,755 40,000 CAF2  404 -503,571 10,819  405 -538,291
15,000 SIO2  406 -11216,000 23,000  407 -289,982 15,000 SIO2  408 1481,373 35,434  409 -212,610 15,000 SIO2  410 -422,622 10,747  411 281,484 10,747 Reflector  (403) 391,580  DM2 Infinity 95,000 Angle 39.degree.  412 304,777 35,000 SIO2  413 -414,139
36,096  414 -217,633 15,000 SIO2  415 291,419 15,871  416 372,431 48,000 SIO2  417 -351,209 1,000  418 478,050 34,000 SIO2  419 -840,313 52,353  420 336,231 20,000 SIO2  421 175,364 55,562  422 -230,487 17,000 SIO2  423 -430,797 1,000  424 648,294 40,000
SIO2  425 -404,757 99,810  426 527,066 30,000 SIO2  427 -13296,000 1,000  428 288,592 22,000 SIO2  429 167,355 54,577  430 -201,179 20,000 SIO2  431 -801,011 103,872  432 -585,801 36,000 SIO2  433 -252,132 1,000  434 457,102 17,000 SIO2  435 260,610
9,580  436 343,579 43,000 SIO2  437 -739,447 1,000  438 226,319 18,500 SIO2  439 173,228 16,103  440 272,220 34,000 SIO2  441 = AP -7972,902 1,000  442 165,067 34,000 SIO2  443 374,040 12,889  444 2219,918 22,000 CAF2  445 -490,695 0,100  446 -715,705
12,000 SIO2  447 134,285 0,100  448 123,907 36,879 SIO2  449 111,965 9,498  450 147,332 35,000 CAF2  451 -967,651 0,100  452 115,241 69,555 SIO2  453 921,256 0,100  454 294,383 28,447 SIO2  455 -500,000 15,000  IM Infinity


 TABLE 4  Lambda = 193,3 nm .beta. = -0,25 NA = 0,7  No. Radius Thickness Glass  0 Infinity 35,000  501 407,048 16,000 SIO2  502 -85814,000 82,000  DM1 Infinity 431,676 Angle 50.degree.  503 524,134 35,000 SIO2  504 -657,304 8,785  505 -587,479
15,000 SIO2  506 1940,811 25,643  507 -324,153 15,000 SIO2  508 -23676,000 37,709  509 -201,728 15,000 SIO2  510 -422,094 12,854  511 282,375 Reflector  (503) 422,676  DM2 Infinity 110,772 Angle 40.degree.  512 373,692 35,000 SIO2  513 -410,297 50,772 
514 -222,817 15,000 SIO2  515 317,101 6,370  516 349,335 48,000 SIO2  517 -362,479 1,000  518 729,698 34,000 SIO2  519 -931,019 57,653  520 371,363 20,000 SIO2  521 210,389 53,764  522 -248,647 17,000 SIO2  523 -428,501 1,000  524 937,198 40,000 SIO2 
525 -388,007 113,824  526 567,461 30,000 SIO2  527 -4351,070 1,000  528 282,352 22,000 SIO2  529 185,586 56,362  530 -234,431 20,000 SIO2  531 -557,904 132,665  532 -408,165 35,442 SIO2  533 -266,966 1,000  534 404,076 17,000 SIO2  535 238,987 14,763 
536 379,049 43,000 SIO2  537 -737,556 1,000  538 245,637 18,500 SIO2  539 178,878 12,206  540 245,508 34,000 SIO2  541 2061,364 10,000  AP Infinity 0,000  542 168,071 34,000 SIO2  543 473,781 9,798  544 1851,461 22,000 CAF2  545 -494,253 0,100  546
-719,297 12,000 SIO2  547 132,814 0,100  548 127,155 34,780 SIO2  549 118,260 11,187  550 169,575 35,000 SIO2  551 -844,545 0,100  552 111,623 74,968 CAF2  553 1756,460 0,100  554 239,829 26,117 CAF2  555 -500,000 15,000  IM Infinity 0,000


 TABLE 5  Lambda = 193,3 nm .beta. = -0,25 NA = 0,7  No. Radius Thickness Glass  0 Infinity 35,000  601 443,397 16,000 SIO2  602 -3263,101 82,000  DM1 Infinity 431,967 Angle 50.degree.  603 510,641 35,000 SIO2  604 -953,685 12,327  605 -534,546
15,000 SIO2  606 1546,359 27,623  607 -295,422 15,000 SIO2  608 -1911,545 32,819  609 -212,072 15,000 SIO2  610 -404,269 12,229  611 279,883 Reflector  (603) 422,967  DM2 Infinity 109,448 Angle 40.degree.  612 338,847 28,000 SIO2  613 -769,850 31,900 
614 1373,814 18,000 SIO2  615 -915,108 37,909  616 -239,573 15,000 SIO2  617 279,202 6,538  618 301,416 46,477 SIO2  619 -437,969 1,000  620 722,212 30,074 SIO2  621 -1063,807 23,211  622 381,419 19,000 SIO2  623 193,859 52,872  624 -235,061 17,000 SIO2 
625 -412,453 1,000  626 990,052 40,000 SIO2  627 -337,530 95,112  628 529,636 30,000 SIO2  629 .sup. .sup. -0,208 1,000  630 264,737 20,000 SIO2  631 173,477 55,898  632 -213,164 19,000 SIO2  633 -478,343 127,971  634 -384,253 29,998 SIO2  635 -241,972
1,000  636 381,178 17,000 SIO2  637 218,858 11,314  638 296,282 43,000 SIO2  639 -966,118 1,000  640 230,570 18,500 SIO2  641 172,880 14,657  642 271,493 30,000 SIO2  643 -49526,000 4,000  AP Infinity 0,000  644 156,048 36,000 SIO2  645 474,860 12,986 
646 -4892,676 20,000 SIO2  647 -452,665 0,100  648 -711,904 34,541 SIO2  649 122,051 9,933  650 171,475 33,021 SIO2  651 -967,318 0,100  652 112,494 72,297 CAF2  653 3642,643 0,100  654 250,427 26,033 CAF2  655 -500,000 15,000  IM Infinity 0,000


 TABLE 6  Lambda = 193,3 nm .beta. = -0,25 NA = 0,7  No. Radius Thickness Glass  0 Infinity 35,000  701 396,818 16,000 SIO2  702 -411120,000 1,000  DP Infinity 85,500 SIO2  DP Infinity 435,933 Angle 50.degree.  703 559,897 35,000 SIO2  704
-763,942 2,707  705 -627,112 15,000 SIO2  706 2056,900 24,065  707 -323,749 15,000 SIO2  708 -4114,500 41,268  709 -197,452 15,000 SIO2  710 -416,693 13,024  711 278,696 Reflector  (703) 420,933  DM2 Infinity 84,857 Angle 40.degree.  712 391,689 35,000
SIO2  713 -391,139 54,674  714 -217,120 15,000 SIO2  715 328,292 6,584  716 363,974 48,000 SIO2  717 -352,092 11,973  718 753,003 34,000 SIO2  719 -915,634 62,045  720 369,054 20,000 SIO2  721 218,165 56,274  722 -247,872 17,000 SIO2  723 -420,231 1,000 
724 970,166 40,000 SIO2  725 -383,655 110,429  726 556,298 30,000 SIO2  727 -5145,200 1,000  728 275,093 22,000 SIO2  729 186,724 57,861  730 -249,939 24,499 SIO2  731 -573,695 138,278  732 -424,514 35,114 SIO2  733 -274,834 1,000  734 391,263 17,000
SIO2  735 226,128 16,728  736 383,272 43,000 SIO2  737 -863,203 1,000  738 239,284 18,500 SIO2  739 178,197 11,299  740 237,727 34,000 SIO2  741 1618,000 10,000  AP Infinity 0,000  742 165,688 34,000 SIO2  743 445,266 9,217  744 1247,900 22,000 CAF2  745
-503,423 0,000  746 -771,731 12,000 SIO2  747 131,678 0,100  748 124,872 29,133 SIO2  749 115,885 13,283  750 179,986 35,000 SIO2  751 -802,711 0,100  752 110,497 77,422 CAF2  753 2393,500 0,100  754 234,953 25,804 CAF2  755 -500,000 15,000  IM Infinity
0,000


 TABLE 7  Lambda = 193 nm .beta. = -0,25 NA = 0,8  No. Radius Thickness Glass  0 Infinity 35,000  801 355,625 15,000 SIO2  802 Infinity 84,000  DM1 Infinity 393,919 Angle 50.degree.  803 621,321 30,000 SIO2  804 17349,000 15,577  805 -522,771
15,000 SIO2  806 7450,061 28,795  807 -279,969 15,000 SIO2  808 -692,552 26,633  809 -231,205 15,000 SIO2  810 -419,760 13,994  811 283,256 Reflector  (803) 384,919  DM2 Infinity 103,131 Angle 40.degree.  812 363,520 35,000 SIO2  813 -312,546 19,745  814
-203,460 15,000 SIO2  815 417,901 4,913  816 637,371 44,999 SIO2  817 -299,660 1,000  818 670,513 36,000 SIO2  819 -607,949 99,443  820 409,543 20,000 SIO2  821 184,175 56,726  822 -190,739 18,000 SIO2  823 -300,666 1,000  824 2541,548 35,000 SIO2  825
-423,211 82,343  826 529,976 40,000 SIO2  827 -575,433 1,000  828 338,904 22,000 SIO2  829 161,992 77,036  830 -180,232 20,000 SIO2  831 -286,886 60,230  832 1358,390 50,000 SIO2  833 -310,335 1,000  834 299,546 17,000 SIO2  835 185,330 22,475  836
318,393 15,000 SIO2  837 240,343 11,470  838 351,936 35,000 SIO2  839 -1892,972 1,000  840 241,744 18,500 SIO2  841 201,167 6,992  842 233,761 35,000 SIO2  843 1187,547 0,000  AP Infinity 6,993  844 173,633 65,000 CAF2  845 -647,630 0,100  846 -1026,314
15,000 SIO2  847 134,041 12,672  848 177,508 43,000 SIO2  849 -552,796 0,100  850 111,087 82,051 CAF2  851 366,445 0,100  852 201,556 9,977 CAF2  853 Infinity 15,000  IM Infinity


 TABLE 8  Lambda 157,000 nm .+-. 2 pm NA = 0,7 .beta. = -0,25  No. Radius Thickness Glass  0 Infinity 35,000  901 509,596 16,000 CAF2  902 -1709,182 82,000  DM1 Infinity 430,770 Angle 50.degree.  903 559,504 35,000 CAF2  904 -1229,460 18,117  905
-727,847 15,000 CAF2  906 1261,260 27,332  907 -297,498 15,000 CAF2  908 -1565,150 32,707  909 -205,835 15,000 CAF2  910 -396,253 12,181  911 279,103 Reflector .phi. 252 mm  (903) 420,578  DM2 Infinity 73,026 Angle 40.degree.  IMI Infinity 34,034  912
341,070 28,000 CAF2  913 -1505,473 32,408  914 969,048 18,000 CAF2  915 -805,764 37,523  916 -248,947 15,000 CAF2  917 286,272 5,893  918 307,931 45,973 CAF2  919 -386,903 1,000  920 1003,377 28,290 CAF2  921 -945,839 20,042  922 397,781 19,000 CAF2  923
197,943 53,200  924 -231,060 17,000 CAF2  925 -406,748 1,000  926 878,953 40,000 CAF2  927 -351,000 100,639  928 481,080 30,000 CAF2  929 11551,730 1,000  930 282,768 20,000 CAF2  931 179,880 51,341  932 -217,737 19,000 CAF2  933 -511,417 127,776  934
-377,857 29,786 .phi.240 mm CAF2  935 -241,099 1,000  936 377,020 17,000 CAF2  937 218,220 11,262  938 299,020 43,000 CAF2  939 -943,927 1,000  940 228,020 18,500 CAF2  941 168,921 13,866  942 263,149 30,000 CAF2  943 -27570,214 0,752  AP Infinity 8,754 
944 157,192 36,000 CAF2  945 476,977 13,281  946 -5291,918 20,000 CAF2  947 -428,700 0,100  948 -634,165 34,624 CAF2  949 123,520 10,454  950 180,781 33,303 CAF2  951 -732,821 0,100  952 115,913 72,125 CAF2  953 3615,409 0,100  954 308,142 25,802 CAF2 
955 -500,000 15,000  IM Infinity  Refractive Indices CaF.sub.2  Lambda = 157,002 157,000 156,998  n = 1,560047 1,560052 1,560057


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DOCUMENT INFO
Description: 1. Field of the InventionThe present invention relates to a projection exposure lens in a projection exposure apparatus such as a wafer scanner or a wafer stepper used to manufacture semiconductor elements or other microstructure devices by photolithography and, moreparticularly, to a catadioptric projection optical lens with an object side catadioptric system, an intermediate image and a refractive lens system for use in such a projection exposure apparatus.2. Related Background ArtU.S. Pat. No. 4,779,966 to Friedman gives an early example of such a lens, however the catadioptric system being arranged on the image side. Its development starting from the principle of a Schupmann achromat is described. It is an issue ofthis patent to avoid a second lens material, consequently all lenses are of fused silica. Light source is not specified, band width is limited to 1 nm.U.S. Pat. No. 5,052,763 to Singh (EP 0 475 020) is another example. Here it is relevant that odd aberrations are substantially corrected separately by each subsystem, wherefore it is preferred that the catadioptric system is a 1:1 system andno lens is arranged between the object and the first deflecting mirror. A shell is placed between the first deflecting mirror and the concave mirror in a position more near to the deflecting mirror. All examples provide only fused silica lenses. NA isextended to 0.7 and a 248 nm excimer laser or others are proposed. Line narrowing of the laser is proposed as sufficient to avoid chromatic correction by use of different lens materials.U.S. Pat. No 5,691,802 to Takahashi is another example, where a first optical element group having positive refracting power between the first deflecting mirror and the concave mirror is requested. This is to reduce the diameter of the mirror,and therefore this positive lens is located near the first deflecting mirror. All examples show a great number of CaF.sub.2 lenses.EP 0 736 789 A to Takahashi is an example, where it